By the time my Uncle John was 28, in the mid-1960s, he had a demanding office job and a young family at home – and it was starting to show.

"I found that I was gaining a couple of pounds a year on home cooking, and getting in the habit of catching a nap after supper," he recalls, "and I realized that I had to get serious about controlling my weight and keeping in shape."

The approach he chose to tackle the problem will sound surprisingly familiar to anyone who's been following the latest exercise science. Body-weight exercises and short bursts of high-intensity exercise are two of the top fitness trends for 2015, according to the American College of Sports Medicine, and they were united in a scientific seven-minute workout popularized by The New York Times in 2013. The combination offers an ultraefficient, convenient, low-tech way to stay in shape – and it's pretty much exactly what has kept Uncle John remarkably trim for nearly 50 years now. The only difference is that his 11-minute routine, first developed by the Royal Canadian Air Force and eventually distributed to 23 million people around the world and translated into 13 languages, is probably better.

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The routine is called 5BX – "five basic exercises" – and it was intended as a way to keep pilots fit even when posted to remote communities with no exercise facilities. At the time, the Department of National Defence estimated that up to one-third of its pilots were physically unfit to fly.

Dr. Bill Orban, the researcher who developed the program in the late fifties, had the then-heretical idea that short bouts of vigorous exercise could be just as effective as longer bouts of moderate exercise for improving fitness. He came up with five basic exercises, four to improve flexibility and strength and one to boost aerobic fitness; none required any equipment at all. A series of charts told you how many of each exercise to do three times a week, and the exercises got progressively harder as you got fitter.

The program was an immediate hit, and not just among pilots. By 1959, The Globe and Mail was reporting that the first printing of 16,000 booklets had sold out; four years later, the tally had reached 5.8 million, including a modified version called XBX aimed at women. Researchers as far afield as Britain and India were soon using 5BX as a standard exercise regimen to study the physiological changes associated with physical fitness.

While 5BX has faded into obscurity, the latest circuit-training routines share many of the same goals. Like Cold War pilots, busy executives are looking for "a simple, fast, science-based workout that can be performed by almost anyone, anywhere, any time, like a hotel room while travelling," says Christopher Jordan, the director of exercise physiology at the Human Performance Institute in Orlando, Fla., who designed the seven-minute workout made famous by the Times.

Jordan first encountered 5BX in the early 1990s as a physiologist with the British Army, and later designed a similar high-intensity circuit program for the U.S. Air Force. The key to benefiting from a single seven-minute session, he says, is reaching near-maximal intensity. If you let the intensity drop, you're better off repeating the seven-minute circuit twice more to get a 21-minute workout.

That's a point echoed by Dr. Martin Gibala, the McMaster University exercise physiologist whose research has demonstrated the aerobic fitness-boosting power of short, high-intensity interval workouts. Most of Gibala's research has focused on intense bursts of cycling, and it's not clear how easily the same aerobic intensities can be reached while doing, say, crunches or squats. "My sense is that the circuit-style body-weight workouts provide a sort of 'happy medium,' inducing some gains in strength that would not be elicited by pure bike or run intervals," he says, "but you likely do not see the same extent of improvement in aerobic conditioning."

And that, it turns out, may be where 5BX has an edge. It allocates two minutes for the first warm-up exercise, then one minute each for the next three strength exercises, and finishes with six minutes of aerobic work – running in place alternating with a series of jumps after every 75 steps. A 24-year-old pilot, for example, would be expected to complete 465 steps mixed with sets of 10 "semi-spread eagle jumps" in six minutes; the civilian standards are a little lower, but your heart will still pound.

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So is there really anything that we, in the Internet Age, can still learn from a half-century-old fitness booklet (the original can be downloaded from the Internet Archive here)?

"There are no secrets," says Dr. Michael Joyner, a physician-researcher at the Mayo Clinic in Minnesota, whose father used 5BX to lose weight in the late 1960s. "There is a tendency to overcomplicate things. 5BX avoids that."

For my uncle, 5BX has played a big part in his life, keeping him fit and helping him, with appropriate adjustments, through several bouts of illness – all for the modest price of 11 minutes a day, three times a week. His parting words of advice, as timeless as 5BX itself: Be consistent.

"If you skip one [session], it's twice as hard to motivate yourself the next day," he says, "and three times as hard the third day."

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